Hetero-Diels–Alder reactions of 2H-phospholes with allenes: synthesis and functionalization of 6-methylene-1-phosphanorbornenes

Abstract

The phospha-Diels–Alder reaction between 2H-phospholes and arylallenes affords 6-methylene-1-phosphanorbornenes in high yields with excellent regioselectivity. This Diels–Alder reaction proceeds at the internal CC double bond of allenes selectively. DFT calculations of possible transition states finely demonstrate the regioselectivity of the reaction. The nucleophilic addition of Ph₂PH to 6-methylene-1-phosphanorbornene sulfides and subsequent desulfurization provide the bidentate phosphine ligands 6, which have a fascinating 1-phosphanorbornene modified PCH₂CH₂P skeleton. The potential applications of 6 as ligands were demonstrated by coordination with transition metals.